Manually remove loom dependency

This is needed to vendor this code into moz-central, see
mozilla/uniffi-rs#1736 for details.

Cargo.toml

@@ -23,13 +23,8 @@ std = []
 # Enables async receiving by implementing Future
 async = []
 
-[target.'cfg(loom)'.dependencies]
-loom = { version = "0.5.3", features = ["futures"] }
-
 [dev-dependencies]
 criterion = "0.3"
-
-[target.'cfg(not(loom))'.dev-dependencies]
 tokio = { version = "1", features = ["rt", "rt-multi-thread", "macros", "time"] }
 async-std = { version = "1", features = ["attributes"] }